Traveling-wave electronic microwave interaction guide devices



KAZUO AYAKl Nov. 24, 1964 Filed Sept. 29, 1960 TRAVELING-WAVE}ELECTRONIC MICROWAVE INTERACTION GUIDE DEVICES FIGS FIG.4

INVENTOR. K A n ki BY five/z 265 14 2147* ATTORNEY United States Patent3,158,779 TRAVELING-WAVE ELECTRONIC MICROWAVE INTERACTION GUIDE DEVICESKazuo Ayaki, Tokyo, Japan, assignor to Nippon Electric Company Limited,Tokyo, Japan Filed Sept. 29, 1960, Ser. No. 59,212 Claims priority,application Japan, Oct. 3, 1959, 34/ 31,442 7 Claims. (Cl. 315-39.3)

This invention relates to electronic microwave signal amplifiers and/oroscillator microwave guide devices, and more particularly toelectromagnetic waveguide devices wherein interaction takes placebetween the electron stream and an electromagnetic wave propagated inthe wave guide, of the type described in Proceedings of the Symposium onElectronic Wave Guides, published in Micro Wave Research InstituteProceedings, Volume 8 of 1958. The wave guide devices of the presentinvention embody all operating elements of such known Wave-guide devicesas described in the aforesaid Proceedings of the Symposium on ElectronicWave Guides except for the modifications of the present invention ashereinafter described.

Travelling Wave tubes, velocity modulation tubes, magnetrons, and thelike, have been heretofore applied as amplifying or oscillating devicesfor microwave signals. The construction of such devices has beenattended with considerable difficulty due to the fact that a slow wavecircuit or cavity resonator becomes smaller in proportion to the wavelength, where the frequency of the signal becomes exceedingly high, forinstance, above 50,000 me.

An important object of the present invention is to eliminate suchdifiiculties. In microwave devices according to the present invention,instead of employing a slow wave circuit or a cavity resonator, usefulinteraction is effected between electromagnetic wave propagation in awave guide and an electron stream therein. The resulting structure issimplified, since there is no slow wave circuit, and it becomes easy toproduce. Several embodiments and the operating principles of the presentinvention are set forth hereinafter, reference being had to theaccompanying drawing, wherein:

FIGS. 1, l-A and 2 show, respectively, the vertical sectionlongitudinally of a microwave device of the present invention, andtransverse cross-sectional views taken along the lines 1A1A and 22 ofFIG. 1;

FIG. 3 illustrates diagrammatically the movement of electrons in thedevice of FIG. 1; and

FIGS. 4, 5 and 6 show transverse cross-sectional views of otherembodiments of the invention.

FIGS. 1, 1-A and 2 illustrate one form of the micro wave device 10 ofthe present invention. The microwave signals are impressed into a waveguide at input side 11; An airtight window 12, of glass for instance, ismounted transversely of the wave guide input 11 in frame 12' therein andsealed in. Window 12 passes the waves along. A- ridge wave guide 13 oftypical cross-section, as shown in FIG. 2, acts as'an anode. The centralregion is a longitudinal, cylindrical passage for microwave signals, asin the TEM mode. axially along the center passage of the anode guide 13.A corresponding window 15 and wave guide terminal 16 are at the outputside of device 10. Ridge wave guide 13 is maintained at a high potentialE-}- with respect to the cathode 14 which emits electrons. Thelongitudinal cathode is preferably a coaxial cylinder, oxidecoated toemit electrons about a coiled heater element with terminals 17, 17'. i

' The device is evacuated Ike a tube, and is operated in the presence ofa magnetic field along the axial direc-' A cathode 14 is positionedtion, indicated by B said field being produced by coil C. Theelectromagnetic signal energy entering from the input wave guide 11performs an interaction with the cathodeemitted electrons along theridge wave guide 13 as it propagates therethrough and goes out from theoutput wave guide 16 after being amplified. The direction of propagationof the electromagnetic signal wave is symmetrical, and can enter fromeither end of the wave guide and go out through the other wave guideend.

FIG. 2 shows a section taken along line 22 of FIG. 1. The cathode 14 ispositioned in the center of the ridge wave guide 13. When the ridge waveguide 13 is maintained at a suitably high potential with respect to thecathode 14, and when a magnetic field B is applied along the axialdirection, the electrons emitted from the cathode 14 revolve around thecathode 14 in a known cycloidal movement. A transverse microwave signal,as a TEM, propagating along the ridge wave guide 13, produces anelectric field a, a, as shown by the lines across ridge gaps 18, 19.When the electrons revolved about the cathode 14 in a cycloidalmovement, arrive at gap 18, they are accelerated. When thehigh-frequency electric field a, a in the gap 18 is of a phase suitablefor accelerating the electrons, they will absorb energy from theelectric field a, a, and thereupon be attracted to the cathode 14,returning to it again, and not continuing the revolving cycloidalmovement.

FIG. 3 illustrates the movement of emitted electrons from cathode 14.The path 20 of the electrons is for those which have been accelerated bythe high-frequency electric field a, a at the gap 18. On the other hand,those electrons which have been slowed or reduced in speed by thehigh-frequency field a, a, at the gap 18, continue their cycloidalrevolution without being returned to cathode 14. The reason for thelatter mode is that such electrons had imparted part of their energy tothe electric field a, a. The path 21 shown, is for electrons that havethus been slowed at the gap 18 by the high-frequency electric field a,a, a cycloidal movement. The impressed electromagnetic wave propagatinglongitudinally along the ridge Wave guide 13 is not slowed down, itsphase velocity actually becoming larger than that of the speed of lightc. Therefore, the phase of the electric field propagating along guide 13by the interaction with the aforesaid electrons at gap 18, will advancemore than several wave lengths during the interval that such electrons(which have gone through a speed reduction by the high-frequencyelectric field a, a at gap 18) will reach the opposite gap 19 throughtheir cycloidal movement.

It is practical to adjust the magnitudes of the accelerating voltage E+for the electrons, the axial magnitude field B, and so forth, so that anoptimum interaction of electrons and propagation of axial waves willoccur, at such phase relation capable of speed-reducing the electrons(in cycloidal movement from the gap 18 to gap 19) through thehigh-frequency electric field that is traveling longitudinally more thanseveral wave lengths behind the phase of the high-frequency electricfield a, a that so acts upon such electrons. When the synchronizedcondition of the applied electromagnetic signal field and the electronstream is satisfied, the emitted electrons will continue to revolvecycloidally, imparting energy to the electromagnetic, field every timethe electrons arrive at gaps 18 and 19, finally arriving at the anode,namely the ridge wave guide 13. In this manner, the applied signalhigh-frequency electromagnetic Wave in the circuit is amplified. If aportion of the amplified output signal, as at 16, is reflected or fedback to the input guide 11, the microwave device 10 will act as anoscillator.

A theoretical explanation of the synchronized condition between theelectrons and the high-frequency electromaglowing equation:

netic field, follows. Reference is made to a related system of theco-pending patent application Serial No. 832,588 filed August 10, 1959,for Microwave Device, by M. Miya, assigned to the assignee of thepresent application; Assuming the angular frequency of theelectromagnetic wave as a, and the revolving angular velocity ofelectrons as w then the necessary time Te for the electrons to travelfrom the gap 18 to gap 19, that is, the time for making a 180 revolutionaround the cathode 14, is expressed as follows:

Te= V (1) Time, Tn, which is the period from the time when the electricfield at the gap is of a phase that reduces the electron speed to thetime when the electric field at the gap 19 is also ofa phase thatreduces the electron speed, is given by the following equation:

where m=0,' 1, 2

The necessary condition that the electrons be in synchronism with theelectromagnetic field, and impart energy to the electromagnetic field,is Te=Tn. Therefore, from Equations 1 and 2, thefollowing Equation 3 isobtained:

This Equation 3 represents the synchronized condition, As is now clearfrom Equation 3, it is feasible to use a value of n that is relativelylarge, even when the frequency used is high and is large. Therefore, theresultant angular velocity of electrons w need not becorrespondinglylarge. The angular velocity w is given approximately bythe fol where V is the accelerating voltage, R and r are the radii ofthe anode and cathode, respectively, and e is the specific charge of theelectrons. Using Equation 4, the synchronized condition of Equation 3can be expressed in terms of the frequency, voltage' and magneticfields, as follows;

' where represents the frequency. From the above equation, it will beunderstood that V and B can beset at practical values only by selectingn to be large, even if f becomes exceedingly large, Say'SOkmc. andabove. V

The present invention is not to be understood as limited to theaforesaid embodiment 10. Thus, the cross-sec be modified as shown inFIGS. 4, Sand 6.

tional configuration of device 10 s shown in FIG. 2, may.

5 The ridge waveguide 13 of FIGS. 1 and 2 contains'two symmetrical,oblong-shaped, longitudinal end regions 22,

thereof results'in 'rather broad-band operation, as an 'amplifierofthe'd evice 10.5For application as' an oscilla- :tof, or special narrowfrequency band amplifier application,-resonant dimensions could beindicated.

" The ridge wave guide corresponding to 13 in device 10 'may assumeconfigurationsas illustrated in FIGSJ 4, 5' and .6, among others. InEEG. '4, the device'Stl, otherwise similar in combination and operationto device 10, has i the cylindrical, longitudinal region Hoff-center ofdevice '30; The cathode 32, however, is central therein; The v i j lowerwall 33 of; the wave guide contains the corresponding cylindrical borefor the axial path. Device 40 has a.

central cathode 41 arrangement, with the side regions 42, 43 oftriangular cross-section. Device 50 has a central cathode 51arrangement, with cylindrical, longitudinal side regions 52, 53.

The microwave device of the present invention is relatively inexpensiveto fabricate, even for exceedingly highfrequency use. It employs nocavity resonator or slow wave circuit sections. Practical, relativelylow values of anode voltage and external magnetic field are feasibleeven for high-frequency operation. Broad-band operation is attainedtherewith.

It will be apparent to those skilled in the art that the novelprinciples of the invention disclosed herein in con-.

nection with specific exemplifications thereof, will suggest variousother modifications and applications of the same.

It is accordingly desired that in construing the breadth of the appendedclaims, they shall not be limited to the specific exemplifications ofthe invention described above.

. I claim:

1. In an electronic microwave guide device, a ridge wave guidecomprising a conductive envelope having an input and an output end; alongitudinal, substantially cylindrical space region and two spaced gapregions extending from and communicating with said space region, and alongitudinal cathode mounted within said longitudinal space region alongthe longitudinal axis of said cylindricalspace region, whereby electronsemitted by said cathode interact with microwave signals propagated alongsaid ridge wave guide to impart amplification energy to the signals;said cylindrical space region and said gap regions communicating'withsaid input and output ends; said cylindrical space region beingcontinuous and substantially straight between said input and outputends; the width of said gap regions adjacentsaid cylindrical spaceregion being substantially less than the diameter of said cylindricalspace region; the length of said gap regions being equal to the lengthof said cylindrical space region.

'2. In an electronic microwave guide device, an input guide element, anoutput guide element, a ridge wave.

guide coupled between said input and output guide elernents andcomprising a conductive envelope having an input and an output end; andcontaining a longitudinal,

substantially cylindrical space region and two spaced gap said gapregions, whereby electrons emitted by said' cathode in the presence of aunidirectional axial'm'ag- 'netic field interact with microwave signalspropagated along said ridge wave guide, with said'guide elementsmaintained atfan anode potential to impart amplification energy to thesignals emergent at said output guide ele-,

ment; said cylindrical space region andsaid gap regions communicatingwith said input and output ends said cylindrical space region beingcontinuous and ,substant ally straight between said input and outputends; the width of said gap regions adjaeentsaid cylindrical spaceregion being substantially less thanthe diameter of said cylindricalspace region; the length'of said'gap regions a being equal to the lengthof said cylindrical spaceregion;

said'gap regions beingsubstant'ially wider; than the diam-. i

eter of said cylindrical, space region at the gap regions remote fromsaid cylindrical space region.

3. In an electronic microwave guide deviceyan input: wave guide and' fan'output'w'ave guide for microwave 1 signals,'a ridge'wave guideintegrally coupled between said input and output wave guides comprisinga conductive envelope having an input and an'outputend; and'includingtwo spaced longitudinal guide'elements containing a longitudinal,substantially.cylindrical space region therebetween i and twospaced gapregions extending from and I communicating with said cylindrical'spaceregion, and a longitudinal cathode mounted concentrically withinlsaidcylindrical space region astride said gap regions, whereby electronsemitted by said cathode in the presence of a unidirectional axialmagnetic field interact with the microwave signals propagated along saidridge wave guide, with said guide elements maintained at an anodepotential to impart amplification energy to the signals emergent at saidoutput wave guide; said cylindrical space region and said gap regionscommunicating with said input and output ends; said cylindrical spaceregion being continuous and substantially straight between said inputand output ends; the width of said gap regions adjacent said cylindricalspace region being substantially less than the diameter of saidcylindrical space region; the length of said gap regions being equal tothe length of said cylindrical space region; said gap regions beingsubstantially Wider than the diameter of said cylindrical space regionat the gap regions remote from said cylindrical space region.

4. In an electronic microwave guide device as claimed in claim 1, awindow sealed-in across each end of the cylindrical space region formaintaining it in an evacuated condition within the device.

5. In an electronic microwave guide device as claimed in claim 3, awindow sealed-in across both said input and output Wave guides formaintaining an evacuated condition within said ridge Wave guide.

6. In an electronic microwave guide device as claimed in claim 1, one ofsaid longitudinal guide elements being integral with an outer wall ofsaid ridge wave guide.

7. In an electronic microwave guide device as claimed in claim 2, one ofsaid longitudinal elements being integral with an outer wall of saidridge wave guide.

References Cited in the file of this patent UNITED STATES PATENTS2,115,521 Fritz et a1. Apr. 26, 1938 2,402,184 Samuel June 18, 19462,406,635 Rarno Aug. 27, 1946 2,414,121 Pierce Jan. 14, 1947 2,542,797Cuccia Feb. 20, 1951 2,698,398 Ginzton Dec. 28, 1954 2,959,707 WilmarthNov. 8, 1960

1. IN AN ELECTRONIC MICROWAVE GUIDE DEVICE, A RIDGE WAVE GUIDE COMPRISING A CONDUCTIVE ENVELOPE HAVING AN INPUT AND AN OUTPUT END; A LONGITUDINAL, SUBSTANTIALLY CYLINDRICAL SPACE REGION AND TWO SPACED GAP REGIONS EXTENDING FROM AND COMMUNICATING WITH SAID SPACE REGION, AND A LONGITUDINAL CATHODE MOUNTED WITHIN SAID LONGITUDINAL SPACE REGION ALONG THE LONGITUDINAL AXIS OF SAID CYLINDRICAL SPACE REGION, WHEREBY ELECTRONS EMITTED BY SAID CATHODE INTERACT WITH MICROWAVE SIGNALS PROPAGATED ALONG SAID RIDGE WAVE GUIDE TO IMPART AMPLIFICATION ENERGY TO THE SIGNALS; SAID CYLINDRICAL SPACE REGION AND SAID GAP REGIONS COMMUNICATING WITH SAID INPUT AND OUTPUT ENDS; SAID CYLINDRICAL SPACE REGION BEING CONTINUOUS AND SUBSTANTIALLY STRAIGHT BETWEEN SAID INPUT AND OUTPUT ENDS; THE WIDTH OF SAID GAP REGIONS ADJACENT SAID CYLINDRICAL SPACE REGION BEING SUBSTANTIALLY LESS THAN THE DIAMETER OF SAID CYLINDRICAL SPACE REGION; THE LENGTH OF SAID GAP REGIONS BEING EQUAL TO THE LENGTH OF SAID CYLINDRICAL SPACE REGION. 